1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for recording a radiation image on a stimulable phosphor, exposing the stimulable phosphor to stimulating rays which cause the stimulable phosphor to emit light in proportion to the stored radiation energy, detecting the emitted light to read out the radiation image, and converting the emitted light into electric signals. This invention particularly relates to a radiation image recording and read-out apparatus which enables selection of use or disuse of a grid device in accordance with an image recording portion of an object or the like.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as the human body to have a radiation image of the object stored thereon, and is then scanned with stimulating rays which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to electric image signals, which are processed as desired to reproduce a visible image having an improved image quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom on a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
Further, in a mobile X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus which is provided with a radiation image recording and read-out apparatus for carrying out the aforesaid radiation image recording and reproducing method and moves from place to place to record radiation images for mass medical examinations, it is disadvantageous to load the mobile X-ray diagnostic station with a large number of stimulable phosphor sheets, and the number of the stimulable phosphor sheets which can be loaded on the mobile X-ray diagnostic station is limited. Therefore, it is desired to load the mobile X-ray diagnostic station with stimulable phosphor sheets which can be used repeatedly, once store the radiation images of the objects respectively on the stimulable phosphor sheets, transfer the electric image signals read out from the stimulable phosphor sheets to a recording medium having a large storage capacity, such as a magnetic tape, and circulate and reuse the stimulable phosphor sheets for further image recording and read-out operations, thereby to obtain the radiation image signals of many objects. Further, when image recording is conducted continuously by circulating and reusing the stimulable phosphor sheets, it becomes possible to increase the image recording speed in mass medical examination. This is very advantageous in practical use.
In order to reuse stimulable phosphor sheets as mentioned above, the radiation energy remaining on the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored thereon should be erased by exposing the stimulable phosphor sheet to light or heat as described in, for example, U.S. Pat. No. 4,400,619 or Japanese Unexamined Patent Publication No. 56(1981)-12599. The stimulable phosphor sheet should then be used again for radiation image recording.
From the aforesaid viewpoint, the applicant proposed in Japanese Unexamined Patent Publication No. 59(1984)-192240 a radiation image recording and read-out apparatus comprising:
(i) a circulation and conveyance means for conveying at least one stimulable phosphor sheet for recording a radiation image thereon along a predetermined circulation path,
(ii) an image recording section disposed on the circulation path for recording a radiation image of an object on the stimulable phosphor sheet by exposing the stimulable phosphor sheet to a radiation passing through the object,
(iii) an image read-out section disposed on the circulation path and provided with a stimulating ray source for emitting stimulating rays for scanning the stimulable phosphor sheet carrying the radiation image stored thereon at the image recording section, and a photoelectric read-out means for detecting light emitted by the stimulable phosphor sheet scanned with the stimulating rays to obtain electric image signals, and
(iv) an erasing section disposed on the circulation path for, prior to the next image recording on the stimulable phosphor sheet for which the image read-out has been carried out at the image read-out section, having the stimulable phosphor sheet release the radiation energy remaining on the stimulable phosphor sheet,
whereby the stimulable phosphor sheet is circulated through the image recording section, the image read-out section and the erasing section, and reused for radiation image recording.
With the radiation image recording and read-out apparatus having such a configuration, the radiation image recording and read-out can be carried out sequentially and efficiently. However, the proposed radiation image recording and read-out apparatus becomes comparatively large because of the provision of the circulation path for the stimulable phosphor sheet in the apparatus.
On the other hand, at the aforesaid image recording section, it is often necessary to use a grid device such as a bucky device, depending on the object portion the image of which is to be recorded. Specifically, in the case where an image of a thick object portion such as the chest is to be recorded, the radiation scattered by the object often causes the image quality to deteriorate. Therefore, in this case, a grid device having a grid for absorbing the scattered radiation, or a bucky device provided with the grid and a means for reciprocally moving the grid should be disposed between the object and the stimulable phosphor sheet. On the other hand, the grid device is not necessary in the case where an image of a thin object portion or the like is to be recorded. Accordingly, it is necessary to mount the grid device on the apparatus and dismount the grid device therefrom in accordance with the image recording portion of the object. However, the grid device is generally large and heavy, and it is very troublesome to repeat mounting and dismounting of the grid device on the apparatus. Also, in the case where a mechanism for mounting and dismounting the grid device is provided, the distance between the object and the stimulable phosphor sheet becomes long, and geometric blur arises.